Suspension system for electric vehicle

ABSTRACT

A suspension system ( 10 ) for a vehicle for suspending a wheel ( 1 ) is disclosed. The suspension system ( 10 ) includes a motor ( 12 ) for driving the wheel of the vehicle; a first suspension ( 22 ) for supporting the wheel ( 1 ) of the vehicle with respect to the vehicle body; a second suspension ( 30 ) for elastically supporting the motor ( 12 ) with respect to the vehicle body; and a power transferring mechanism ( 14 ) for transferring power from the motor ( 12 ) to the wheel ( 1 ) while permitting relative movement of the motor ( 12 ) with respect to the wheel ( 1 ).

TECHNICAL FIELD

The present invention relates to a suspension system for a vehicle thatutilizes the power of motors for driving wheels.

BACKGROUND ART

JP2000-16040 A discloses a suspension system for use in a vehicle,wherein a motor for driving the wheel is provided inside the wheel. Withthis arrangement, thanks to arranging the motor within the wheel, it ispossible to make advantageous use of space within the wheel as well asto reduce the weight of a mechanism for transferring the driving powergenerated from the motor to the wheel.

In this conventional suspension system, since the motor is directlyconnected to the wheel, an unsprung mass increases by the amount of themotor and components associated therewith, resulting in a deteriorationin a road holding characteristic and thus ride quality.

DISCLOSURE OF INVENTION

Therefore, it is an object of the present invention to improve ridequality of a vehicle that utilizes power of a motor for driving a wheel.

In order to achieve the above-mentioned objects, according to one aspectof the present invention a suspension system for a vehicle is provided,comprising: a motor for driving a wheel of the vehicle; a firstsuspension for supporting the wheel of the vehicle with respect to avehicle body; a second suspension for elastically supporting the motorwith respect to the vehicle body; and a power transferring mechanism fortransferring power from the motor to the wheel while permitting relativemovement of the motor with respect to the wheel.

According to this aspect of the present invention, the motor is notrigidly supported with respect to the wheel or rigidly supported withrespect to the vehicle body but is elastically supported with respect tothe vehicle body by the second suspension. Since the motor and the wheelare supported independently by the first and second suspensions,respectively, with respect to the vehicle body, an unsprung mass isreduced, resulting in improvement in a road holding characteristic.

In a particular embodiment, the second suspension includes a springelement and a damper element. With this embodiment, it is possible togive particular suspension characteristics suited for the motor and thewheel to the suspensions for the motor and the wheel, respectively. Inother words, it is possible to tune the respective characteristics(spring/damper property) of the first and second suspensionsindependently.

In a particular embodiment, a damper element of the first suspension andthe damper element of the second suspension are interconnected via afluid passage such that the motor and the wheel move in opposite phases.With this embodiment, when the wheel bounds or rebounds, the wheel andthe motor are forced to move in opposite directions (in oppositephases), whereby a vibration-damping effect can be attained. It is notedthat through the fluid passage is circulated a fluid (gas, oil, etc.)filling a fluid cylinder.

In another particular embodiment, the damper elements of the secondsuspensions on both sides (i.e. left side and right side) of the vehicleare interconnected via a fluid passage. With this embodiment, it ispossible to limit the movements of the motors on the both sides of thevehicle to an in-phase mode or an opposite-phase mode. For example, incase of limiting the movements to an in-phase mode, since the movementsof the motors in up-and-down directions are permitted only when theunsprung components on both sides of the vehicle vibrates in phase, itis possible to prevent sprung mass from being urged in a roll directiondue to reaction forces of the motors.

According to another aspect of the present invention a suspension systemfor a vehicle is provided, comprising: a motor for driving a wheel ofthe vehicle; a first suspension for supporting the motor with respect toa vehicle body such that the motor can move in up-and-down directionswith respect to the vehicle body; a second suspension for supporting thewheel with respect to the motor such that the wheel can move inup-and-down directions with respect the motor; and a power transferringmechanism for transferring power from the motor to the wheel whilepermitting relative movement of the motor with respect to the wheel.

According to this aspect of the present invention, since the motor andthe wheel are dependently supported by the first and the secondsuspensions, respectively, a road holding characteristic is improvedwith respect to an arrangement in which the motor and the wheel areinterconnected rigidly and supported by a suspension simultaneously.

In a particular embodiment, the first suspension includes a springelement and a damper element and the second suspension includes a springelement and a damper element. With this embodiment, it is possible togive particular suspension characteristics suited for the motor and thewheel to the suspensions for the motor and the wheel, respectively. Inother words, it is possible to tune the respective characteristics(spring/damper property) of the first and second suspensionsindependently.

In another particular embodiment, the first suspension includes a leafspring. With this embodiment, it is possible to simplify the secondsuspension.

Other objects, features and advantages of the present invention willbecome more apparent from the following detailed description when readin conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic front view of a first embodiment of a suspensionsystem according to the present invention.

FIG. 2 is a view of a support mechanism for a motor 12 as seen from adirection X of FIG. 1.

FIG. 3A is a diagram for illustrating a spring-mass model of thesuspension system 10 according to the present invention.

FIGS. 3B and 3C are diagrams for illustrating traditional spring-massmodels for comparison purposes.

FIG. 4 is a graph showing performances of the spring-mass modelsillustrated in FIGS. 3A-3C.

FIG. 5 is a schematic front view of a second embodiment of a suspensionsystem according to the present invention.

FIG. 6 is a schematic front view of a third embodiment of a suspensionsystem according to the present invention.

FIG. 7 is a schematic perspective view of a fourth embodiment of asuspension system according to the present invention.

FIG. 8 is a diagram for schematically illustrating the connectionstructure between the motor 12 and the gear casing 52 of FIG. 7.

FIG. 9A is a diagram for illustrating a spring-mass model of thesuspension system 10 of FIG. 7 according to the present invention.

FIG. 9B is a diagram for illustrating a traditional spring-mass modelfor comparison purposes.

FIG. 10 is a graph showing performances of the spring-mass modelsillustrated in FIGS. 9A-9B.

FIG. 11 is a schematic front view of a fifth embodiment of a suspensionsystem according to the present invention.

FIG. 12 is a schematic front view of a sixth embodiment of a suspensionsystem according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereafter, the preferred embodiments according to the present inventionare explained with reference to the drawings.

FIG. 1 is a schematic front view of a first embodiment of a suspensionsystem according to the present invention. The suspension system 10according to this embodiment has a motor 12 for driving a wheel. Everydriven wheel is provided with one of the motors 12 and a braking system(e.g., a caliper and a disk rotor) shown in part. A steering system(e.g., a tie rod) is provided for steering the wheel. Explanation ismade below for only one driven wheel, since there is substantially nodifference in arrangement between the wheels. However, it is noted thatthe arrangement according to this embodiment may be applied to onlyfront wheels or only rear wheels.

A rotating shaft of the motor 12 is connected to the driven wheel via adrive shaft (including a constant velocity joint) 14 that passes througha knuckle (steering knuckle) 20. The drive shaft 14 is rotatablysupported inside the knuckle 20 by way of a bearing 16. To the knuckle20 is coupled a lower end of a suspension 22 which mainly includes acoil spring and a shock absorber. An upper end of the suspension 22 isconnected to a vehicle body. To the knuckle 20 is also coupled one endof a lower arm 24 via a ball joint. The other end of lower arm 24 ispivotally mounted to the vehicle body. In this way, the driven wheel issupported by the vehicle body such that it can move mainly inup-and-down directions with respect to the vehicle body via thesuspension 22.

FIG. 2 is a view of a support mechanism for the motor 12, as seen from adirection X of FIG. 1. The motor 12 according to this embodiment issupported by the vehicle body via a suspension 30 such that it can movemainly in up-and-down directions with respect to the vehicle body, asshown in FIG. 1. The suspension 30 illustrated in FIG. 1 includes ashock absorber and a coil spring integrated therewith. Preferably, themotor 12 is supported by way of two suspensions 30, which are arrangedin parallel, so as not to be rotated when a rotating counterforce isapplied thereto, as shown in FIG. 2. Typically, the two suspensions 30have the same spring and shock-absorbing characteristics. In this case,the two suspensions 30 are disposed along the circumference of the motor12 and coupled to the motor 12 (an outer casing of motor 12) at the twopoints 40 set thereon. It is noted that the motor 12 is disposed asclose to the driven wheel as possible in order to shorten the length andthus reduce the weight of the power transferring mechanism including aconstant velocity joint and so on.

With this arrangement, the motor 12 is supported by the vehicle bodysuch that it can move mainly in up-and-down directions with respect tothe vehicle body via the suspensions 30. In this way, the motor 12 andthe wheel shaft 18 have corresponding centers of gravity, which move inup-and-down directions independently from each other. Concerning this,the power transferring mechanism (constant velocity joint), whichprovides the coupling between the rotating shaft of the motor 12 and thewheel shaft 18, is configured to accommodate such relative movementbetween the motor 12 and the wheel shaft 18 as well as to transfer therotating torque generated by the motor 12 to the wheel shaft 18.

It is noted that the present invention should not be limited by theaforementioned configuration for coupling the motor 12 to the wheelshaft 18 or the aforementioned configuration for suspending the drivenwheel. Different configurations may be applicable as long as theyprovide the motor 12 and the driven wheel with such elastic supportswith respect to the vehicle body, which enable the motor 12 and thedriven wheel to move in up-and-down directions independently from eachother while enabling the transfer of the driving power of the motor 12to the wheel shaft 18. For example, the present invention can be appliedto any type of suspension system other than the strut type suspensionabove-mentioned, such as a double wishbone type suspension and the like.Further, the motor 12 may be connected to the driven wheel via aflexible coupling.

FIG. 3A shows a spring-mass model of the suspension system 10 accordingto the present invention. FIG. 3B shows a comparative spring-mass modelof the suspension system 10 where the motor 12 is rigidly coupled to thevehicle body. FIG. 3C shows another comparative spring-mass model of thesuspension system 10 where the motor 12 is directly coupled to thewheel. FIG. 4 shows performance curves (acceleration in up-and-downdirections versus frequency) of the respective spring-mass models inFIGS. 3A-3C compared under the same conditions (as to the mass of acomponent, a spring constant, etc.).

According to the present embodiment, as is apparent from the foregoingor FIGS. 3A-3C, since the motor 12 is connected to the vehicle bodyindependently from the driven wheel, the unsprung mass is the same asthat of the configuration shown in the FIG. 3B and smaller than that ofthe configuration shown in the FIG. 3C by the mass of the motor 12 (plusthe masses of components associated with motor 12). Therefore, with thepresent embodiment, as indicated by a solid line in FIG. 4, a roadholding characteristic at the resonance frequency of the unsprung massis significantly improved with respect to the configuration (indicatedby a break line in FIG. 4) shown in the FIG. 3C. Further, according tothe present embodiment, since the motor 12 is supported by the vehiclebody via the springs and the shock absorbers, a road holdingcharacteristic at the resonance frequency of the sprung mass is alsoimproved to a certain degree with respect to the configuration(indicated by alternate long and short dashed lines in FIG. 4) shown inthe FIG. 3B.

Consequently, according to the present embodiment, since the motor 12 isnot one of the unsprung components, the unsprung mass is reduced, whichimproves the road holding characteristic. Further, it is possible totune suspension characteristics for the motor 12 and the driven wheelindependently, because they are suspended independently with respect tothe vehicle body. Further, since the motor 12 is supported by thevehicle body via the springs and the shock absorbers, it is possible toprevent the vibrations of the motor 12, which are vibrations generatedby the rotating operation or by the driving over a bad road, from beingtransferred to the vehicle body

It is noted that the suspension 22 for the driven wheel and/or thesuspension 30 for the motor 12 may be constituted by a leaf springinstead of the spring and the shock absorber.

Next, a second embodiment of a suspension system 10 according to thepresent invention is described with reference to FIG. 5. FIG. 5 is aschematic front view of a suspension system 10 according to the secondembodiment. Explanation is made below for only one wheel, since there issubstantially no difference in arrangement between the wheels. However,it is noted that the arrangement according to this embodiment may beapplied to only front wheels or only rear wheels.

As shown in FIG. 5, the suspension system 10 according to the secondembodiment differs from the suspension system 10 according to the firstembodiment in that a fluid passage 32 (e.g., a pipe or tubing) connectsan appropriate fluid chamber 22 a of the shock absorber of thesuspension 22 for the driven wheel, which may be one of 2 fluid chambersdefined by a piston within a piston cylinder, to an appropriate fluidchamber 30 a of the shock absorber of the suspension 30 for the motor12. In this embodiment, the fluid passage 32 establishes fluidcommunication between the shock absorber of the suspension 22 and theshock absorber of the suspension 30 such that the two fluid chambers 22a and 30 a displace (expand and contract) in opposite phases. Thus, whenthe driven wheel bounds, for instance, the fluid in the fluid chamber 22a on the driven wheel side is discharged into the fluid chamber 30 a onthe motor 12 side via the fluid passage 32, whereby the motor 12 movesin a downward direction (the direction in which the volume of the fluidchamber 30 a increases). In this way, according to this embodiment, themotor 12 and the driven wheel are forced to move in opposite phases, byway of which a vibration-damping effect is attained.

It is noted that in the case of the two suspensions 30 being providedfor each driven wheel as abovementioned, two fluid chambers 30 a of therespective suspensions 30 may be independently connected to the fluidchamber 22 a via two fluid passages 32. Alternatively, two fluidchambers of the respective suspensions 30 may be connected to each othervia a separate fluid passage in such a way that the two fluid chambersinvoluntarily move in phase and then one fluid chamber of the two fluidchambers may be connected to the fluid chamber 22 a on the driven wheelside via the fluid passage 32 in such a manner as abovementioned. It isalso noted that the present invention can be applied to any type ofshock absorber such as an air type or oil type one, and a one-way typeor two-way type one.

Next, a third embodiment of a suspension system 10 according to thepresent invention is described with reference to FIG. 6. FIG. 6 is aschematic front view of a suspension system 10 according to the thirdembodiment. It is noted that the arrangement according to thisembodiment may be applied to only front wheels or only rear wheels.

As shown in FIG. 6, the suspension system 10 according to the thirdembodiment differs from the suspension system 10 according to the firstembodiment in that appropriate fluid chambers 30 aL, 30 aR of the shockabsorbers of the suspensions 30L, 30R on both sides of the vehicle areconnected to each other via a fluid passage 34. In this embodiment, thefluid passage 34 establishes fluid communication between the shockabsorbers of the suspensions. 30L, 30R on both sides of the vehicle suchthat the two fluid chambers 30 aL and 30 aR displace (expand andcontract) in phase. Thus, when the motor 12L for the driven wheel on theleft side moves in an upward direction (the direction in which thevolume of the fluid chamber 30 aL decreases), the fluid in the fluidchamber 30 aL of the suspension 30L on the left side is discharged intothe fluid chamber 30 aR of the suspension 30R on the right side via thefluid passage 34, whereby the motor 12R on the right side is urged in anupward direction (the direction in which a volume of the fluid chamber30 aR increases). In this way, since the motors 12L, 12R on both sidesof the vehicle are permitted to move in up-and-down directions only inphase, the movements of the motors 12L, 12R in up-and-down directionsare permitted only when the unsprung components on both sides of thevehicle vibrate in phase. As a result of this, it is possible toeffectively prevent sprung masse from being urged in a roll directiondue to reaction forces of the motors 12L, 12R.

It is noted that in the case of the two suspensions 30 being providedfor each driven wheel as abovementioned, two pairs of two fluid chambersof the shock absorbers on both sides of the vehicle are connected viatwo fluid passages 34 in such a manner as abovementioned. Alternatively,two fluid chambers of the shock absorbers on each side may be connectedto each other via a separate fluid passage in such that the two fluidchambers involuntarily move in phase and then one fluid chamber of thetwo fluid chambers on one side may be connected to one of the two fluidchambers on the other side via the fluid passage 34 in such a manner asabovementioned.

It is noted that the fluid passage 34 may establish fluid communicationbetween the shock absorbers of the suspensions 30L, 30R on both sides ofthe vehicle such that the two fluid chambers 30 aL and 30 aR displace inopposite phases instead of in the same phase.

Next, a fourth embodiment of a suspension system 10 according to thepresent invention is described with reference to FIGS. 7 and 8.

FIG. 7 is a schematic perspective view of the suspension system 10according to this embodiment. The suspension system 10 according to thisembodiment has a motor 12 for driving a wheel. Every driven wheel isprovided with the motor 12 and a braking system (e.g., a brake shoe 50,etc.) shown in part. A steering system (e.g., a tie rod 54) is providedfor steering the wheel. Explanation is made below for only one wheel,since there is substantially no difference in arrangement between thewheels. However, it is noted that the arrangement according to thisembodiment may be applied to only front wheels or only rear wheels.

The motor 12 according to this embodiment is supported by the vehiclebody via a suspension 30, which includes a shock absorber and a coilspring, such that the motor 12 can move in up-and-down directions withrespect to the vehicle body, as shown in FIG. 7. To the motor 12 isconnected a gear casing 52 which transfers power from the motor 12 tothe wheel. A rotating shaft (output shaft) 13 of the motor 12 (see FIG.8) is adapted to the gear casing 52.

To the gear casing 52 is connected a hub unit 60. The hub unit 60supports the wheel shaft by way of a bearing (not shown) incorporatedtherein. The wheel shaft of the driven wheel is supported within thegear casing 52 by way of a bearing (not shown). The gear casing 52 has adriving mechanism such as a driving chain and a driving belt which iswound around the wheel shaft and the rotating shaft 13. In this way, therotating torque generated by the motor 12 can be transferred to thewheel shaft of the driven wheel via the driving mechanism.

A part 15 of the rotating shaft 13 of the motor 12, which corresponds toa portion with smaller radius in the illustrated embodiment, issupported rotatably by a bearing (not shown) incorporated in the gearcasing 52, as shown in FIG. 8. This bearing of the gear casing 52permits rotation of the rotating shaft 13 while carrying axial andradial loads between the gear casing 52 and the rotating shaft 13. Tothe gear casing 52 is attached one end of a lower arm 24. The other endof the lower arm 24 is pivotally mounted to a suspension member (thevehicle body) by way of a bushing and the like. With this arrangement,the gear casing 52 is permitted to rotate around the rotating shaft 13of the motor 12 while transferring power from the motor 12 to the wheelshaft. Correspondingly, the hub unit 60 is also permitted to rotatearound the rotating shaft 13 of the motor 12 together with the gearcasing 52.

Between the gear casing 52 and the motor 12 is provided a suspension 22.The suspension 22 illustrated in FIG. 7 includes a shock absorber and acoil spring incorporated therein. The upper end of the suspension 22 iscoupled to a shell member (a lower spring seat for the coil spring) ofthe suspension 30 for the motor 12. The upper end of the suspension 22may be coupled to other portions that move together with the motor 12.

The lower end of the suspension 22 is connected to the gear casing 52(in this case, an inner surface of the gear casing 52). With thisarrangement, the hub unit 60 including a tire, a wheel, a brake, etc.,that is connected to the gear casing 52 is supported via the suspension22 such that the hub unit 60 can move mainly in up-and-down directionswith respect to the motor 12. Preferably, the connection point of thelower end of the suspension 22 to the gear casing 52 has an adequatedistance from the rotational center (corresponding to the rotating shaft13 of the motor 12) of the gear casing 52 in order to efficiently dampenthe vibrations of the hub unit 60 in up-and-down directions.

It is noted that the present invention should not be limited by theaforementioned suspending way for the hub unit 60. Any suspending waysis applicable as long as the hub unit 60 including a tire, a wheel, abrake, etc., is elastically supported such that the hub unit 60 can movemainly in up-and-down directions with respect to the motor 12. Forexample, the suspension 22 may be arranged between the hub unit 60 andthe motor 12 or any portion that moves together with the motor 12.

FIG. 9A shows a spring-mass model of the suspension system 10 accordingto this embodiment. FIG. 9B shows a spring-mass model of the suspensionsystem 10 for comparison purposes, where the motor 12 is rigidly coupledto the vehicle body. FIG. 10 shows performance curves (acceleration inup-and-down directions versus frequency) of the respective spring-massmodels in FIGS. 3A-3B (a solid line for FIG. 3A and a broken line forFIG. 3B).

According to the present embodiment, as is apparent from the foregoingor FIGS. 3A-3B, the motor 12 and the hub unit 60 are connected to thevehicle body in series via respective spring elements and respectivedamper elements. Although this configuration defines two resonancepoints of an unsprung mass, a road holding characteristic (a ridecomfort characteristic) at the higher resonance point is significantlyimproved with respect to the configuration shown in FIG. 9B, as shown inFIG. 10. Further, since the motor 12 and the hub unit 60 are suspendedindependently by the respective suspensions 22, 30, it is possible totune suspension characteristics for the motor 12 and the hub unit 60independently.

Next, a fifth embodiment of a suspension system 10 according to thepresent invention is described with reference to FIG. 11. FIG. 11 is aschematic front view of the suspension system 10 according to fifthembodiment. Explanation is made below for only one wheel, since there issubstantially no difference in arrangement between the wheels. However,it is noted that the arrangement according to this embodiment may beapplied to only front wheels or only rear wheels.

The suspension system 10 according to this embodiment is embodied byapplying the present invention to a known strut type suspension system.Specifically, a suspension 22 is disposed between a hub unit 60 and amotor 12, the same as the fourth embodiment. Similarly, the upper end ofthe suspension 22 is coupled to a shell member (a lower spring seat forthe coil spring) of the suspension 30 for the motor 12. Similarly, theupper end of the suspension 22 may be coupled to other portions thatmove together with the motor 12, instead of the shell member. The lowerend of the suspension 22 is coupled to a knuckle arm of the hub unit 60.In this arrangement, the hub unit 60 including a tire, a wheel, a brake,etc., is supported such that it can move mainly in up-and-downdirections with respect to the motor 12.

The motor 12 is supported by a suspension 30 such that it can movemainly in up-and-down directions with respect to the vehicle body. Arotating shaft (output shaft) 13 of the motor 12 (see FIG. 8) and awheel shaft of the driven wheel are interconnected via a flexiblecoupling 62. The flexible coupling 62 transfers power from the motor 12to the wheel shaft while permitting relative movement between the motor12 and the wheel shaft.

Correspondingly, according to this embodiment, since the hub unit 60(including a tire, a wheel, a brake, etc.) is elastically supported suchthat it can move mainly in up-and-down directions with respect to themotor 12, and the motor 12 is elastically supported such that it canmove mainly in up-and-down directions with respect to the vehicle body,a road holding characteristic is improved with respect to aconfiguration in which the hub unit 60 is rigidly connected to the motor12.

Next, a sixth embodiment of a suspension system 10 according to thepresent invention is described with reference to FIG. 12. FIG. 12 is aschematic front view of the suspension system 10 according to sixthembodiment. Explanation is made below for only one wheel, since there issubstantially no difference in arrangement between the wheels. However,it is noted that the arrangement according to this embodiment may beapplied to only front wheels or only rear wheels.

The suspension system 10 according to this embodiment applies thepresent invention to a known double wishbone type suspension.Specifically, to a hub unit 60 is coupled a lower arm 24 and an upperarm 25 via ball joints or the like. The other ends of the lower arm 24and the upper arm 25 are pivotally mounted to the vehicle body viabushings or the like.

Between the hub unit 60 and the motor 12 are provided a shock absorber64 and a plate spring 66. One end of the shock absorber 64 is coupled toa shell member (a lower spring seat for the coil spring) of thesuspension 30 and the other end is coupled to a knuckle arm of the hubunit 60. In this arrangement, the hub unit 60 including a tire, a wheel,a brake, etc., is supported by the shock absorber 64 and the platespring 66 such that it can move mainly in up-and-down directions withrespect to the motor 12.

A rotating shaft (output shaft) 13 of the motor 12 and a wheel shaft ofthe driven wheel are interconnected via a drive shaft 63 including aconstant velocity joint. The drive shaft 63 transfers power from themotor 12 to the wheel shaft while permitting relative movement betweenthe motor 12 and the wheel shaft.

Similarly, according to this embodiment, since the hub unit 60(including a tire, a wheel, a brake, etc.) is elastically supported suchthat it can move mainly in up-and-down directions with respect to themotor 12, and the motor 12 is elastically supported such that it canmove mainly in up-and-down directions with respect to the vehicle body,a road holding characteristic is improved with respect to aconfiguration in which the hub unit 60 is rigidly connected to the motor12.

It is noted that the shock absorber 64 may be omitted if the platespring 66 is a leaf spring (a laminated spring) that has a requireddamper characteristic. This arrangement can simplify means forsupporting the hub unit 60 so that it can move mainly in up-and-downdirections with respect to the motor 12.

The present invention is disclosed with reference to the preferredembodiments. However, it should be understood that the present inventionis not limited to the above-described embodiments, and variations andmodifications may be made without departing from the scope of thepresent invention.

For example, in the aforementioned fourth and fifth embodiments, thesuspension 22 for the hub unit 60 and/or the suspension 30 for the motor12 may be constituted by a leaf spring instead of the spring and theshock absorber. Further, the shock absorber may be any type of shockabsorber such as a air type or oil type one, and a one-way type ortwo-way type one.

Further, in the aforementioned fifth embodiment, the rotating shaft 13of the motor 12 and the wheel shaft of the driven wheel may beinterconnected via a constant velocity joint. Similarly, in theaforementioned sixth embodiment, the rotating shaft 13 of the motor 12and the wheel shaft of the driven wheel may be interconnected via aflexible coupling.

1. A suspension system for a vehicle, comprising: a motor that isdisposed between a vehicle body and a knuckle for driving a wheel; afirst suspension that is provided between the wheel and the vehicle bodyfor elastically supporting the wheel of the vehicle with respect to thevehicle body; a second suspension that is provided between the motor andthe vehicle body for elastically supporting the motor and providingindependent movement of the motor with respect to the vehicle body; anda power transferring mechanism that is provided between a rotating shaftof the motor and a wheel shaft of the wheel for transferring power fromthe motor to the wheel while permitting relative movement of the motorwith respect to the wheel, wherein the second suspension includes aspring element and a damper element.
 2. A suspension system for avehicle, comprising: a motor for driving a wheel of the vehicle; a firstsuspension for supporting the wheel of the vehicle with respect to avehicle body; a second suspension for elastically supporting the motorwith respect to the vehicle body; and a power transferring mechanism fortransferring power from the motor to the wheel while permitting relativemovement of the motor with respect to the wheel, wherein a damperelement of the first suspension and a damper element of the secondsuspension are interconnected via a fluid passage.
 3. A suspensionsystem for a vehicle, comprising: a motor for driving a wheel of thevehicle; a first suspension for supporting the wheel of the vehicle withrespect to a vehicle body; a second suspension for elasticallysupporting the motor with respect to the vehicle body; and a powertransferring mechanism for transferring power from the motor to thewheel while permitting relative movement of the motor with respect tothe wheel, wherein damper elements of second suspensions on both sidesof the vehicle are interconnected via a fluid passage.
 4. A suspensionsystem for a vehicle, comprising: a motor that is disposed between avehicle body and a knuckle for driving a wheel; a first suspension thatis provided between the motor and the vehicle body for supporting themotor with respect to the vehicle body such that the motor can move inup-and-down directions with respect to the vehicle body; a secondsuspension that is provided between the wheel and the motor forsupporting the wheel with respect to the motor such that the wheel canmove in up-and-down directions with respect to the motor; and a powertransferring mechanism that is provided between a rotating shaft of themotor and a wheel shaft of the wheel for transferring power from themotor to the wheel while permitting relative movement of the motor withrespect to the wheel.
 5. The suspension system as claimed in claim 4,wherein the first suspension includes a spring element and a damperelement and the second suspension includes another spring element andanother damper element.
 6. The suspension system as claimed in claim 4,wherein the first suspension includes a plate spring.
 7. A suspensionsystem for a vehicle, comprising: a motor that is disposed between avehicle body and a knuckle for driving a wheel; a first suspension thatis provided between the wheel and the vehicle body for elasticallysupporting the wheel of the vehicle with respect to the vehicle body; asecond suspension that is provided between the motor and the vehiclebody for elastically supporting the motor and providing travel of themotor with respect to the vehicle body; and a power transferringmechanism that is provided between a rotating shaft of the motor and awheel shaft of the wheel for transferring power from the motor to thewheel while permitting relative movement of the motor with respect tothe wheel.